Image Processing System and Log Storage Method

1. An image processing system including a terminal device and an image processing apparatus that are connected and communicated with an external storage medium respectively, wherein: the terminal device comprises: a file creation unit operable to create a file including identification information of the external storage medium associated with a public key and store the file in the external storage medium, when the terminal device is connected with the external storage medium, and a decryption unit operable to decrypt an encrypted log using a secret key corresponding to the public key, when the terminal device is connected with the external storage medium storing the encrypted log; and the image processing apparatus comprises: an identification information determination unit operable to determine whether or not the identification information of the external storage medium is identical with the identification information in the file, when the image processing apparatus is connected with the external storage medium storing the file, an encryption unit operable to encrypt a log using the public key stored in the file of the external storage medium and store the encrypted log in the external storage medium, when it is determined that the identification information of the external storage medium is identical with the identification information in the file, and a termination unit operable to stop a use of the image processing apparatus when it is determined that the identification information of the external storage medium is not identical with the identification information in the file.

2. The image processing system according to claim 1 , wherein the file creation unit creates a table associating the secret key with the identification information previously registered in the external storage medium and stores the table in a specific memory in the terminal device, when the terminal device is connected with the external storage medium, and the decryption unit refers to the table storing the identification information corresponding to the identification information of the external storage medium and decrypts the encrypted log using the secret key in the table, when the terminal device is reconnected with the external storage medium storing the encrypted log.

3. The image processing system according to claim 1 , wherein the file creation encrypts the file using a common key common to the external storage medium and the terminal device and stores the encrypted file, when the terminal device is connected with the external storage medium, and the encryption unit, when the image processing apparatus is connected with the external storage medium storing the file encrypted by the common key, decrypts the encrypted file using the common key, obtains the public key, and executes the encryption.

4. The image processing system according to claim 1 , wherein the public key and the secret key are one-time keys.

5. An image processing system according to claim 1 , further comprising an available term determination unit in the image processing apparatus, wherein the file creation unit determines an available term for storing the log in the external storage medium, and stores a file including the identification information and the available term in the external storage medium, the available term determination unit determines whether or not a current time is in the available term when the identification information of the external storage medium is identical with the identification information in the file, and the encryption unit encrypts the log in the image processing apparatus when the current time is in the available term, and stores the encrypted log in the external storage medium.

6. The image processing system according to claim 1 , wherein the termination unit stops the use of the image processing apparatus when the identification information of the external storage medium is not identical with the identification information in the file, and gives an alarm, sends the alarm to the terminal device, or displays an error message on a touch panel of the image processing apparatus.

7. The image processing system according to claim 2 , further comprising a termination unit in the image processing apparatus, wherein the termination unit displays, on a liquid crystal display of the terminal device, a message that the external storage medium is illegal, and stops the image processing apparatus, when the identification information of the external storage medium is not identical with the identification information in the table.

8. A log storage method for an image processing system including a terminal device and an image processing apparatus that are connected and communicated with an external storage medium respectively, comprising steps of: creating a file including identification information of the external storage medium associated with a public key and storing the file in the external storage medium, when the terminal device is connected with the external storage medium, using the terminal device; determining whether or not the identification information of the external storage medium is identical with the identification information in the file, when the image processing apparatus is connected with the external storage medium storing the file, using the image processing apparatus; encrypting a log using the public key stored in the file of the external storage medium and storing the encrypted log in the external storage medium, when it is determined that the identification information of the external storage medium is identical with the identification information in the file, using the image processing apparatus; stopping a use of the image processing apparatus when it is determined that the identification information of the external storage medium is not identical with the identification information in the file, using the image processing apparatus; and decrypting the encrypted log using a secret key corresponding to the public key, when the terminal device is reconnected with the external storage medium storing the encrypted log, using the terminal device.